Typically, a linear olefin having 9 or more carbon atoms, which is to be dehydrogenated, is a valued compound that is widely utilized as a basic material for intermediates for preparing biodegradable detergents, medicines, plastics, synthetic rubber and the like. Methods of producing linear olefin from linear paraffin having 9 to 13 or more carbon atoms through dehydrogenation are known, and generally include bringing hydrogen and gaseous paraffin into contact with a dehydrogenation catalyst, followed by reaction at a high temperature under atmospheric pressure. In the dehydrogenation reaction system, the catalyst has been prepared to mainly increase the rate of reaction and simultaneously inhibit side reactions such as pyrolysis, coke production, isomerization, etc. so as to increase the linear olefin selectivity.
A dehydrogenation catalyst, which is commonly useful for producing linear olefin from linear paraffin, is mainly prepared by impregnating silica, alumina, or silica-alumina with a Group VIII precious metal such as platinum or the like. Such a catalyst is problematic because metal particles may be sintered early due to the high temperature in the initial stage of the reaction, undesirably shortening the lifetime of the catalyst. In order to increase the activity of the catalyst for dehydrogenating linear paraffin, the olefin selectivity, and the lifetime of the catalyst, useful is a catalyst configured such that a Group VIII precious metal such as platinum or the like is coupled with one or more other metals selected from among tin, lithium, potassium, sodium, etc. Meanwhile, in the reaction mechanism for dehydrogenating a paraffinic hydrocarbon, the reaction progresses at a high temperature, and thus, not only the dehydrogenation reaction but also side reactions such as pyrolysis and coke production may occur, undesirably lowering catalytic activity and selectivity. Particularly in the case of a catalyst configured such that the active metal is deeply incorporated into the support, total dispersibility becomes good, and thus, even when the reactant is incorporated into the support through material transfer and diffusion, it comes into contact with the active metal sites, thus increasing the total activity. However, the reactant or product may reside in the catalyst for an excessively long period of time, undesirably causing side reactions such as adsorption of the product inside the catalyst, additional reaction of products, isomerization and coke production, and shortening the lifetime of the catalyst. Hence, thorough research is ongoing into distribution of the active metal inside the support to suppress side reactions in the dehydrogenation reaction and to increase the produced olefin selectivity. In particular, there are proposed methods for disposing the active metal on the outer surface of the catalyst support to minimize the material transfer effect, and to increase the selectivity and maximize the activity while minimizing the contact time between the reactant and the catalyst.
For example, U.S. Pat. Nos. 4,077,912 and 4,255,253 disclose a catalyst prepared by coating a support with a catalytic metal oxide, thus enabling incorporation to the outer surface of the support, and U.S. Pat. No. 6,177,381 discloses a catalyst where, in order to prevent the diffusion of an active metal into the support upon loading of the active metal, alpha alumina and cordierite are used as the inner core, and gamma alumina and active metal are mixed to give a slurry which is then used to form an outer layer, thereby increasing the selectivity and the extent of dehydrogenation using the catalyst. The above patent also discloses that the slurry for forming the outer layer is mixed together with the active metal, after which the resulting mixture may be applied on the inner core, or alternatively that the slurry may be applied and the active metal may then be loaded thereon.